Transient spectroscopic studies of charge carrier dynamics in organic solar cells

Organic solar cells (OSCs) are one of the promising third-generation lightweight and flexible photovoltaics. Since the 1990s, the development of OSCs can be described in three phases. In the first phase, the ‘bulk heterojunction’ concept was established. From the 2000s, the second phase focused on pairing different polymers with fullerene derivatives, following the observation of ultrafast electron transfer from polymer donors to fullerene acceptors. Most recently, in the third phase, the development of non-fullerene acceptors has led to a surge in the efficiency. While the material design has been driving such developments, photophysical understandings of the mechanisms are still lagging yet are crucial towards the evolution of OSCs. This thesis describes an experimental investigation into the functional mechanisms of charge generation, separation, and recombination processes in non-fullerene based OSCs by steady-state and transient spectroscopies. Chapter 3 and 4 investigate the carrier dynamics in polymer:non-fullerene bulk heterojunction OSCs with small driving forces for charge separation, probing their particular photophysics. Specifically, Chapter 3 shows that charge-transfer state recombination becomes more severe in a low-offset system. This analysis has been extended to six other systems in Chapter 4, suggesting that the lifetime of charge-transfer states becomes shorter as their energetics are suppressed. Chapter 5 and Chapter 6 focus on the carrier dynamics in homojunction OSCs employing small molecules. While bulk heterojunction OSCs are currently leading the efficiency, homojunction OSCs are still attractive due to their enhanced device stability and high photovoltages. Chapter 5 shows that the molecular electrostatics arising from different molecular orientations drives charge separation in a sexithiophene pristine film, leading to efficient charge photogeneration in devices. In contrast, Chapter 6 attributes the origin for charge generation in naphthalocyanine based devices to the built-in field, meaning no sign of charge generation is observed in pristine films. Finally, the impact of these two charge generation pathways on the carrier dynamics in planar heterojunction OSCs employing the aforementioned two materials is investigated. Overall, this thesis examines the impacts of the driving force, molecular electrostatics and electric field on charge generation, separation, and recombination processes in both heterojunction and homojunction OSCs. The unique findings within this thesis have unlocked greater understandings of the fundamental mechanisms of charge generation in OSCs and it is hoped that this will aid in the design of future material systems.Open Acces

Algorithm-Directed Crash Consistence in Non-Volatile Memory for HPC

Fault tolerance is one of the major design goals for HPC. The emergence of non-volatile memories (NVM) provides a solution to build fault tolerant HPC. Data in NVM-based main memory are not lost when the system crashes because of the non-volatility nature of NVM. However, because of volatile caches, data must be logged and explicitly flushed from caches into NVM to ensure consistence and correctness before crashes, which can cause large runtime overhead. In this paper, we introduce an algorithm-based method to establish crash consistence in NVM for HPC applications. We slightly extend application data structures or sparsely flush cache blocks, which introduce ignorable runtime overhead. Such extension or cache flushing allows us to use algorithm knowledge to \textit{reason} data consistence or correct inconsistent data when the application crashes. We demonstrate the effectiveness of our method for three algorithms, including an iterative solver, dense matrix multiplication, and Monte-Carlo simulation. Based on comprehensive performance evaluation on a variety of test environments, we demonstrate that our approach has very small runtime overhead (at most 8.2\% and less than 3\% in most cases), much smaller than that of traditional checkpoint, while having the same or less recomputation cost.Comment: 12 page

A dual-cameras-based driver gaze mapping system with an application on non-driving activities monitoring

Characterisation of the driver's non-driving activities (NDAs) is of great importance to the design of the take-over control strategy in Level 3 automation. Gaze estimation is a typical approach to monitor the driver's behaviour since the eye gaze is normally engaged with the human activities. However, current eye gaze tracking techniques are either costly or intrusive which limits their applicability in vehicles. This paper proposes a low-cost and non-intrusive dual-cameras based gaze mapping system that visualises the driver's gaze using a heat map. The challenges introduced by complex head movement during NDAs and camera distortion are addressed by proposing a nonlinear polynomial model to establish the relationship between the face features and eye gaze on the simulated driver's view. The Root Mean Square Error of this system in the in-vehicle experiment for the X and Y direction is 7.80±5.99 pixel and 4.64±3.47 pixel respectively with the image resolution of 1440 x 1080 pixels. This system is successfully demonstrated to evaluate three NDAs with visual attention. This technique, acting as a generic tool to monitor driver's visual attention, will have wide applications on NDA characterisation for intelligent design of take over strategy and driving environment awareness for current and future automated vehicles

Effects of SOCS3 on the development of colon cancer via regulation of HIF-1α

Purpose: To investigate the influence of suppressor of cytokine signaling 3 (SOCS3) on rats with colon cancer (CC). Methods: Sprague-Dawley (SD) rats were randomly divided into CC group and control group, and then CC rat model was constructed. The expression of SOCS3 in CC tissues was determined by quantitative real time-polymerase chain reaction (qRT-PCR). Hematoxylin-eosin staining (H&E) was used to examine colon tissue morphology. Immunohistochemistry (IHC) staining assay was performed to determine the expression of SOCS3 protein in colon tissues. The contents of HIF-1α, phosphorylated phosphatidylinositol 3-hydroxy kinase (p-PI3K), and phosphorylated protein kinase B (p-AKT) proteins were determined by Western blotting (WB). Results: Compared with that in the control group, the number of tumors in CC group was significantly increased (p < 0.05). 2). On the other hand, protein and message ribonucleic acid (mRNA) expressions of SOCS3 were down-regulated in CC group (p < 0.05). 3), while protein expressions of p-PI3K, p-AKT and HIF-1α were raised in CC group (p < 0.05). Conclusion: SOCS3 is lowly expressed in CC rats, and promotes the expression of HIF-1α by activating PI3K/AKT signaling pathway. Thus, SOCS3 provides a therapeutic strategy for the management of colon cancer. Keywords: Colon cancer; Suppressor of cytokine signaling protein 3 (SOCS3); Hypoxia inducible factor-1